U.S. Geological Survey Data Series 773
Included below are trackline maps, which represent the vessel position during the survey; the navigation data used to create these maps have not been corrected for the offset between the GPS antenna and the boomer's transducer (figure 2). The trackline maps were created with ESRI ArcGIS 10 software, exported to Adobe Illustrator for further editing, and saved in JPEG format. These images can be accessed through the link provided below or from within the maps folder. For more information about the GIS project, refer to the Software page.
NOTE: Navigation data were recorded to two different sections of the SEG Y trace headers, creating two navigation datasets. The navigation data written to the "Source coordinates" trace headers (bytes 73 - 80) are only accurate within 1 s of arc, or about 31 m. Additional navigation data were recorded more accurately to the "Unassigned" trace headers (bytes 181 - 240) by the acquisition software (Delph Seismic); these data were not used to create the trackline maps. Links to these files are provided below in the Raw Shotpoint Navigation section.
Location Map
99FGS01 Location Map
99FGS02 Location Map
In addition to raw shotpoint navigation files, 500-shot-interval files were generated to help correlate shot locations on the map with evenly spaced 500-shot index markers along the top of the printable profile images. Both shotpoint navigation files and 500-shot-interval location files were extracted from the trace headers of each line using SU software and the readll script (refer to the boomll.tar (69-KB) tape archive, which can be found in the su folder). Shotpoint coordinates were then projected from latitude and longitude coordinates to UTM northings and eastings (WGS84, Zone 17, meters) using PROJ.4 software (http://trac.osgeo.org/proj/) and reformatted for use with ESRI GIS software. A file containing the location of the start of each line was also created for use on the trackline maps. The processed navigation data have not been corrected for the offsets between the shotpoint and GPS antenna (fig. 2).
The processed shotpoint navigation and 500-shot-interval location files can be accessed through the links provided below or from within the nav folder. Each ASCII text file contains eight fields separated by commas and defined as follows:
Field 1: UTM X (Zone 17)
Field 2: UTM Y (Zone 17)
Field 3: Trackline Number
Field 4: Shotpoint Number
Field 5: Longitude (decimal degrees)
Field 6: Latitude (decimal degrees)
Field 7: Year
Field 8: Day of Year:Hour:Minute:Second (UTC)
99fgs01.txt - Processed Shotpoint Navigation (8.6-MB ASCII text file)
s99fgs01.txt - Processed 500-Shot-Interval Location Navigation (730-KB ASCII text file)
99fgs02.txt - Processed Shotpoint Navigation (3.3-MB ASCII text file)
s99fgs02.txt - Processed 500-Shot-Interval Location Navigation (7.0-KB ASCII text file)
Shotpoint navigation files were extracted from the trace headers of each line using SU software. Unprocessed navigation files are stored as ASCII text files in the rawnav folder by trackline number. These navigation data have not been corrected for the offset between the shotpoint and GPS antenna. Each file contains six fields separated by a space and defined as follows:
Field 1: Trackline Number
Field 2: Shotpoint Number
Field 3: Longitude (decimal degrees)
Field 4: Latitude (decimal degrees)
Field 5: Year
Field 6: Day of Year:Hour:Minute:Second (UTC)
The navigation data extracted from the "unassigned" trace headers can be found in the delphnav folder along with the navigation driver files associated with the navigation system.
